System of automatic offset control for traffic signals



3,0 75,1 73 CL FOR Jan. 22, 1963 J. N. PAUL SYSTEM OF AUTOMATIC OFFSET CONTR TRAFFIC SIGNALS 2 Sheets-Sheet 1 PHIGHWHY Filed July 1, 1959 OUTBOUND l 05 (OFFSET SELECTOR) 29(Zafcb) SYSTEM OF AUTOMATIC OFFSET \CONTROL FOR TRAFFEC SHGNALS Joseph N. Paul, Norwallr, Cont-1., assignor, by mesne assignments, to The Gameweli tlompany, Newton, Mass, a corporation at Delaware Filed .luiy l, 1959, Ser. No. 824,373 10 Qlairns. (Cl. 3419-38) This invention relates in general to improvements in electrical circuits and devices for controlling signalling apparatus, and especially for controlling a plurality of signals arranged in a coordinated group or system.

Tratiic moves most efiiciently in what is known as a progressive system, and in setting up such as system provision must be made for dividing the time at each intersection in a manner best suited to accommodate the trafiic, and provision must also be made for setting the relative timing of offsets of the green indications. Progressive systems are in common use, some of which provide a selection of offsets to adapt the apparatus to changes in trafiic and some provide a limited selection of timing divisions or splits, and some provide means for changing the cycle length, these adjustment or manipulations being possible by remote control from a central station.

This invention is directed more specifically to improvements in offset control. It includes many of the advantages as set forth in my application Serial No. 793,710, filed February 17, 1959, for System of Automatic Offset Control for Traffic Signals, such as low cost, ready application as independent or satellite controls or providing more than the usual three or four offsets.

Further objects and advantages will be pointed out or become apparent as the description proceeds.

in the accompanying drawings:

FIG. 1 is a diagram showing a form of control apparatus embodying the inevntion;

FIG. 2 is a block diagram showing the equipment indicated in FIG. 1;

FIG. 3 is a diagram showing a modification of the control apparatus shown in FIG. 1; and

FIG. 4 is a block diagram showing the equipment indicated in FIG. 1 as connected into a complete signal system.

The diagram of FIG. 1 has been prepared in an acrossthe-line form in which the main lines of the power supply P and C are shown at the left and right sides respectively. At the upper part of FIG. 1 is represented a highway with arrows indicating the outbound and inbound trafiic lanes. A detector D is shown in the outbound trafiic lane and a detector DI is shown in the inbound trafiic lane. Below the detectors are shown schematically two time element relays IE0 and TEI connected into the circuits from detectors DO and DI respectively. In the power feed to the detectors is shown schematically the usual transformer TR to provide a voltage convenient for use in the detectors. Below the time element relays and transformer is shown offset selector OS, and below this, latch relays LRI and LRO.

The offset selector OS is a unit in which R represents the rotor of a motor (the well known induction disk type bein assumed as convenient) equipped with four driving elements 11, 12, 13 and 14 of the well known shading pole piece type. These driving elements are each arranged to produce torque on the rotor in the direction indicated by the accompanying arrows. The adjustable shading pole pieces are preferably equipped with dials indicating their positions which gives an indication of the torque being produced. Dials are occasionally omitted to prevent unauthorized adjustments, making it necessary twi 73 21, shown for convenience on cam 7, comes in contact with fixed stop 22 limiting the rotation of the cam shaft.

When the cam shaft is stopped in this manner, the

motor is intentionally stalled. The motor used is of a wellknown type that will not be harmed by repeated or continuous stalling.

LRl and LRO are commercial available latch relays. They control circuits 2 and 3 as will be described later.

The diagram FIG. 2 shows, in block form, the controller shown in FIG. 1. Detectors DO and DI feed into ofiset selector OS through connections 122 and 123 respectively. Offset selector OS feeds latch relays LRI and LED through connections 125 and 126 respectively.

atch relay LRl feeds offset control line 3 and latch relay LRO feeds offset control line 2.

The diagram PEG. 3 is a modification of FIG. 1. It should be noted that cam of FIG. 3 and all parts to the left of this cam in the diagram including the detectors and associated parts are the same as in FIG. 1 and carry I the same references. The four cams 2&5, 2%, 2&9 and 210 and their associated connections are modified, the latch relays are eliminated and lines 2 and 3 are fed directly from contacts in the modified oifset selector M08. The relative advantages of the disclosures of FIGS 1 and 3 will be compared later.

FIG. 4 is a block diagram showing my invention in an oiiset controller as associated with other units to make up a complete operating system. The master controller MC may be any of the various types used to establish and maintain the cycle length for the system. It may be of the so-called pre-timed type in which no provision is made for change in cycle length but preferably is of a type providing cycle length adjustment by trafiic actuation, by a program instru cut or by manual manipulation. The offset controller OC shown in block form consists of the same units shown in the wiring diagram of FIG. 1 and is subject to the modification shown by FIG. 3. The local signal controller LSC may be any one of the various types available that will respond to changes in offset, a preferred type being as disclosed in my Patent No. 2,657,375. The signals S may be of any approved type.

Referring to FIG. 1, we may assume for convenience of explanation that all parts are in positions as shown, which will be referred to as the neutral position. In operation the equipment, as will be explained, has forces acting to return the cam shaft to the neutral position, and in this connection the neutral position is referred to as the homing position. This is the condition that would be established by no traiiic or by evenly balanced tra'liic in both directions on the highway. Contacts in detectors DI and D0 are open, contacts .15, i6, 19 and 29 are all open, contacts 17 and 1b are both closed, but a small movement of the cam shaft 36 in a clockwise direction would open contact 1? but contact 13 would remain closed. Similarly a small movement of cam shaft 36 in a counterclockwise direction would open contact 18 and contact 17 would remain closed. A slight overlapping of the closed positions of contacts 17 and 18, while not necessary, is desirable for reasons explained later. All contacts on latch relays LRI and LRO are open under the conditions assumed.

A vehicle actuating a detector usually closes the detector contact for a very short time as each axle passes.

. This time is too short to perform the desired function with the equipment being described so the impulse of the first axle of a vehicle passing a detector is used to initiate a time period of a length convenient to apply a current to a driving element of rotor R to obtain the action desired Time element relays TEI and IE are inserted between the detectors and the motor coils to lengthen the detector impulses to about two seconds each. Additional axles on a vehicle usually pass during this lengthened period and are inetieetive. In the present example it is assumed that each vehicle causes one effective impulse in passing each detector. Exceptions would be rare and negligible;

Assume now for example that with all parts in the positions shown in FIG; 1, a car actuates detector DE. This will momentarily close the contact in detector DI and complete the circuit from power supply line P through lead 52. transformer TR lead 88, detector DI and lead 56 to time element relay TEI, which in turn will feed an impulse of convenient length of two'seconds, for example, through lead 57, driving element 11 and through lead 54 to power supply line C. This produces a torque in rotor R'in a clockwise direction as shown by the accompanying arrow. At the time in this example that driving element 11 became energized, driving element 13 was energized by the circuit from power supply line P through'lead 1%, contact 17, lead 92, driving element. '13 and lead 54 to power supply line 6, and driving element 14 was energized by the circuit from power supply line P through lead 1%, contact 18, lead 93, driving element 14 and lead 54 to power supply line C.

-Driving elements fiend 14 are adjusted to produce relatively weak torques each sufiicient to slowly rotate rotor R unaided if unopposed. Driving elements 11 and 12 are adjusted to produce relatively strong torques sufficient to rotate rotor R in the direction of the accompanying arrows even when opposed by the torques of driving elements 14 and 13 respectively.

As explained above the actuation of detector DI causes driving element 11 to be ener ized for a period assumed, for example, to be two seconds. During this time rotor R will be moved an increment of rotation in a clockwise direction against the opposition of driving element 14. It will be observed that at the start of this" increment of rotation driving element 13 will be acting in a clockwise direction but in a short time will be cut off by the opentug of contact 17. This effect of driving element 13 to aid rotation of rotor R in a clockwisedirection is so relatively short that it is inapprcciable and will be disregarded in this and future examples. Rotation of cam shaft 36 in a clockwise direction will, however, hold-contact 18 closed and driving element 14 will continue to exert torque in a counterclockwise direction. This torque, if unopposed, will rotate cam shaft 36 in a counterclockwise direction to its homing position in a restoration time assumed, for example, to be seconds. Thus, if no cars after the one assumed actuate detector DI before the end of this restoration period, the efiect of the one car will be cancelled. Contacts 15 and 16 will not change positions during this increment of movement of cam shaft 36. Contacts 19 and 29 control the release coils of the latch re lays but a breaking or reenergizing of these circuits does not change anything in the controlled circuits unless in the meantime the relay-operating coils have been energized. The operation of contacts 15, 16, 19 and 29 and the latch relays will be explained later.

Assume now that starting with all parts in the neutral position, as shown in FIG. 1, a car actuates detector DI and that before driving element 14 has returned cam shaft 36 to the neutral position a second car also actuates detector DI. This will rotate cam shaft 36 an increment in a clockwise direction which will be added to the uncancelled portion of the previous increment. The amount ofthis uncancelled portion of increment will depend upon the time interval between the two cars. It now additional cars actuate detector Dial: a rate faster than driving element 14 can cancel this effect on clockwise rotation of cam shaft 36, the increments or portions of increments of rotation will be cumulative so that eventually cam shaft 36 will be rotated clockwise until limited by engagement of stop pin 21 with stop 22.

In the above no mention was made of detector DO and its associated parts. It was assumed that there were no actuations of detector DO and that driving element 12 associated with detector DO was inactive.

The operation of detector D0 is the same as explained for detector DI. A car actuating detector D0 will complete the circuit from power supply line P through lead 52, transformer TR, lead 1&4, detector DO, lead '76, time element TEO, lead 77, drivingelement 12 and lead 54- to power supply; line C. This operation will energize driving element 12 for an impulse which will be assumed as two seconds in length just as was assumed for driving element 11. During this time rotor R will be moved an increment of rotation in a counterclockwise direction against the opposition of driving element 13. The effect of driving element 14 to aid driving element 112 is of such short duration that it may be disregarded just as a similar eiiect of driving element 14; was disregarded. Torque exertedby driving element 13, if unopposed, will return cam shaft 3610 the homing position just as driving element 14 restores cam shaft 36 to the homing position, as explained. It additional cars actuate detector DO at a rate faster than driving element 13, can cancel their effect, the accumulated efiect of counterclockwise rotation of cam shaft 36 will. continue until camshaft 36 is stalled by stop pin 21, coming in contact with stop 22.

Theoverall effect of a car actuating detector DI is to exert a driving force on cam shaft 36 in a clockwise direction. The overall. effect of a car actuating detector DO isto exert a driving force on cam shaft 36 in a counterclockwise direction. These effects have been explained when cars are actuating one detector only. Normal traffic moves in both directions in a highway but in varying volumes. This condition will now be considered.

Assume for. convenience that all parts are inthe neutral position, as shown in FTG. 1, andthat an inbound car aetuates detector DI simultaneously with an outbound car actuating detector DO. The inbound car will cause an incrementof torque to drive cam shaft 36 in a-clockwise direction and the outbound car will cause an increment of torque to drive cam shaft 36 in a counterclockwise di rection. It is assumed that the two opposing increments are equal in which case they would balance and cancel each other so there would be no movement of cam shaft 3&5.v

Assume now that a car actuates' detector DI and that three. seconds later a car actuates detector DO. The action set up by the car actuating detector D1 will be to cause atwo second increment of torque in driving element llwhich will cause an increment of rotation of cam shaft 3o in a clockwise direction. This movement will be against theopposing torque of driving element 14 as previously explained. At the end of the assumed three sec ends the actuation of detector D0 will cause an increment of, torque in driving element 12 acting to drive cam shaft 36 in a counterclockwise direction and will add to the torque ,of driving elementl l, hastening the return of cam shaft 36 to the neutral position. In this assumption as in the previous one the efiects ofthe single cars actuating their respective detectors will cancel each other.

Assume nowthat cars actuate detector DI at the heavy rate of 20 cars per minute and that cars actuate detector DO at a relatively lower rate of 10 cars per minute. The relativelylarger portion of the timethat driving element Dl is energiz ed will produce sufiicient torque in driving element llto overbalance the combined opposing torques of driving elements 12 and 14 and the cam shaft 36 will in' a period of time,'the limits of which will be described later, rotate in aclockwise direction until stop pin 21 engages stop 22. i in this position of the cam shaft earn 5 will close contact 15, completing the circuit from power supply line P through lead res, contact 15, lead 82, coil 23 and lead 55 to power supply line C. This energizes relay coil 23 which closes contacts 27 and 39 and energizes line 2 from power supply line P through lead 84, lead 97 and Contact 27. When contacts .27 and 39 in latch relay LRI are once closed they are held in the closed position by latch 29 and will remain closed until latch 29 is released by energizing release coil 25. Energizing line 2 as above selects the offset favoring inbound trafiic by means well known in the art.

t has been explained how a car actuating an inbound detector can cancel the effect of a car actuating an outbound detector how these actuations can be simul taneous, overlapping or not overlapping. It has been found that with equipment made in accordance with the disclosure of this invention that the above cancelling effect is near enough to uniform to be accepted as uniform throughout the normal ranges of traffic density.

in a coordinated traific control system of the type now under consideration trafiic forms into groups or platoons as they are often called. A platoon forms for each signal cycle with spaces between in which time cross trafiic moves. To obtain a fair average rate of trafic flow, it is usually advisable to average at least three platoons or take an average over a period of time of approximately six minutes. The present invention is unique as far as I can determine in that it does not use any timed sampling period to measure rate of traflic flow, but uses a more desirable means of comparing traffic flow in two oppositely moving lanes by computing the preponderance of trafiic flow in on lane compared to the other and selecting oifsets best suited to this preponderance or to a relative lack of preponderance.

For convenience let us refer to the resultant effect of a detector actuation, by a passing car, as a detector impulse. In the above example it was assumed that driving element 11 received detector impulses at the rate 0f 20 per minute that driving element 12 received detector irn ulses at the rate of l@ per minute. Under this assumption driving element ll. would receive a preponderance of detector impulses at the rate of per minute. To determine this rate of traffic how with reasonable accuracy detector impulses should be considered over a longer period than one minute. Let us assume a minimum time of three minutes. The offset selector would then be adjusted so that a preponderance of detector impulses at the rate of 10 per minute for a total of 3t: in three minutes would cause cam shaft 36 to turn from the neutral position to its extreme clockwise position in three minutes. Any other ratio of inbound and outbound traffic, such as to 5, for example, that would produce the same preponderance in the same time would have the same resultant action on the offset selector.

Assume now a traffic condition in which driving element 11 receives detector impulses at the rate of 18 per minute and that [driving element 12 receives impulses at the rate of it) per minute. Under this assumption driving element ll would receive a preponderance of detector impulses at the rate of 8 per minute or 24 in three minutes. At this rate the torque produced by driving element 11 will be proportionally less compared to the opposing torques of driving elements 12 and 14- but with normal adjustments will still drive cam shaft 36 in a clockwise direction until stop pin -11 engages stop 22 but a longer time of approximately four minutes will be required. If the preponderance of detector impulses received by driving element 11 is further reduced, the time required for cam shaft 3; to be driven in a clockwise direction to the limiting position where stop pin 21 engages stop 22 will increase until a balance is reached where driving element 31 can not overcome the opposition of driving elements 12- and 14%. This balance point can be easily controlled by adjustment of control dials on driving elements 11, 12 and 1 If the preponderance of detector impulses on (driving element ll falls below the balance point, the combined torques of driving elements 12 and 14 will overcome the torque of driving element if, and cam shaft 36 will rotate in a counterclockwise direction. If this rotation continues until cam 9 closes contact 19, the circuit will then be closed from power supply line P through lead res, contact 19, lead till, lead lill, coil 25, and lead to power supply line C. This will energize coil 25 which will cause latch 2.9 to release contacts 27 and 39 to their open positions. Line 2 will then be deenergized by the breaking of its power supply through contact 27. Deenergizing line 2 selects the orfset favoring balanced trafiic by means well known in the art.

Assume now an example in which all assumptions for tratlic flow are the same as in the preceding examples except that the directions of traffic flow are reversed. Assumptions for actuations formerly applied to detector D1 will now be applied to detector DO and assumptions for actuations formerly applied to detector D0 will now be applied to Di. The functioning of driving elements 11 and 12 will be substituted for each other and in a like .ianner the functioning of driving elements 13 and 1 5 will be interchanged. This will substitute counterclockwise rotation of cam shaft so for clockwise rotation and the functioning of cam ii for cam 7, cam 6 for cam 5 and earn it) for cam 9. This will substitute the functioning of latch relay LRO and its connections for latch relay LRI and its connections and substitute energizing line 3 instead of line 2. This will be the condition for selecting offset favoring outbound traflic by means well known in the art. if there is insufficient preponderance of trafic in either direction to select a favoring offset, selection will revert to an offset for balanced traffic. The ranges of these selections are easily adjusted by adjustment of the shading pole pieces on the four driving elements 11, 12, 13 and is.

In the preceding examples and descriptions, contacts 33 and 4% have performed no functions. They do not function in normal operation and may be omitted with their associated connections, leads 1%, 58, 69 and N2. They do, however, provide a safety feature. it is common practice to have relays jack mounted and it is also common practice for service and maintenance men to remove these relays from their jacks for inspection. In replacing these relays the error could easily be made of having the contacts of both relays latched in the closed position. This would cause lines 2 and 3, which are controlled by the relays as explained, to be closed at the same time which would cause great confusion in the system. The confusion would during the course of normal traiiic changes correct the error but it would be possible for the confusion to last several hours and :delay a large number of cars.

The safety feature which is recommended consists of the circuit from power supply line P through lead 109, contact 39, lead 58, lead 63, coil 26 and lead 55 to power supply line C. Thus when contact 39 of latch relay LRI is closed, release coil 26 of relay LRO is energized which will open contact 2? and deeuergize line 3. Similarly when contact as is closed, the circuit will be completed from power supply line P through lead 6?, contact 40, lead 162, lead fill, coil 25 and lead 55 to power supply line C. Thus when contact 46* of latch relay LRO is closed, release coil 25 of relay LRI is energized which will open contact 27 and deenergize line 2. This safety feature will, therefore, immediately correct any error in leaving latch relays LRO and LRI both latched at the same time.

Refer now to FIG. 3. It will be observed that many of the parts are the same as in FIG. 1 and carry the same reference numbers. These parts include the highway with its detectors and associated parts, rotor R and its associated parts, and cams 7 and 8 and their associated parts. Cam shaft 236 of FIG. 3 is driven in exactly the same manner as cam shaft as of FIG. 1 so all examples used to explain the rotation of cam shaft 36 of FIG. 1 i may be applied to the rotation of cam shaft 236 of FIG. 3. The modification shown in FIG. 3 is in the four cams shown on the right of cam shaft 236 and the control of lines 2 and 3 without latch relays LM and LED.

Cam 2-05 is rotatably mounted on cam shaft 236 with a bearing permitting turning with a minimum of friction but restricted from moving along the shaft. Cam 2%6 is held fast to cam shaft 236. Pin 255 is mounted on cam 2&5 and lies in a notch 2% of cam 296 and drives cam 2455 when engaged with cam 206. The friction of finger 225 by hearing on cam 20 5 is sufficient to hold earn 2% against the friction of its hearing but will permit carn 2G5 to be driven when pin 255 engages cam 2%.

Assume the position of all parts as shown in FIG. 3 and that cam shaft 236 is then driven in a clockwise direction. Cam 2% will move with cam shaft 236 but, until cam ace engages pin 255, cam 2% will be held stationary by the friction of finger 225. After a time predetermined by its shape and adjustment, earn 2% will engage pin 255 and drive cam 295 to the position where finger 225 drops into the notch in earn 265, thus closing contact 215 and energizing line 2 from power supply line P through lead 306 and contact 215. This operation is equivalent to the closing of contact in FIG. 1 which in turn energizes line 2 through latch relay LRI as explained. This is the condition brought about in both FIGS. 1 and 3 by a preponderance of inbound trafiic and selects the oifset to favor the condition.

Assume now that the preponderance of inbound trafiic decreases to the point to drive cam shaft 236 in a counterclockwise clirection, Cam 205 will disengage pin 255 and cam 205 will not move until cam 206 engages pin 255 in the counterclockwise direction. After a space of movement of cam shaft 236, cam 296 will engage pin 255 and turn cam 265 to break contact 215 which will deenergize line 2. This corresponds to the deenergizing of line 2 in FIG. 1 by the closing of contact 19 which energizes coil 25 and opens contact 27. A suficient preponderance of outbound traffic will rotate cam shaft 236 just as explained for FIG. 1 and will energize and deenergijze line 3 by the closing and opening of contact 216 which is closed and opened by the action of cams 2&9 and 210 and pin 259; The overall results of operation of apparatus FIG. 1 and FIG. 3 are the same.

Apparatus FIG. 3 has the advantage of eliminating latch relays LRI and LRO, thus simplifying the equipment and reducing the cost although the cams of FIG. 3 might be slightly higher in cost. Apparatus FIG. 3 has the disadvantage that the contacts 215 and 216 that control the outgoing circuits may have a tendency to flutter, making the time of make and break a little uncertain and also tending to burn the contacts.

Apparatus FIG. 1 has the advantage that outgoing lines 2 and 3 are closed, held closed, and are opened by positiveacting contacts. Contacts 15, 16, 19 and 20 of FIG. 1 are subject to fluttering the same as all contacts operatedby slow moving cams but the contacts on the relays which they control are either closedor opened on the first impulse of a flutter and then latch in position where they are not affected by fluttering of the operating circuits. Also by controlling lines 2 and} by relay contacts the offset selector is protected from damage byline surges of power to which all long control lines are exposed. Damage to relays by such surges is usually less costly than to such a device as an olfset selector.

FIG. 4 shows a master controller MC for controlling the cycle length butit should be noted that the operation of offset selector OS is entirely independent of the master controller and the signal cycle length.

-In FIGS. 1 to 4 inclusive a highway has been indicated and referred to as having a single lane of trafic for each direction. In multiple lane highways which are in common use actuations representative of traflic flow may be easily obtained by placing detectors in each active lane and connecting them in parallel to the respective time element relays. The time intervals of the time element relays would then be shortened to allow a fair average to be recorded and the offset detector dials would be adjusted to respond to this traflic and select oifsets just as explained for a single lane. It is true that simultaneous passings of cars in parallel lanes would register a single impulse and that cars in parallel lanes would cause partly overlapping impulses but apparatus according to this invention inherently averages these overlapping impulses into an accurate working average. Three important characteristics of the induction diskmotor, with its shading pole piece drives, work to even out these averages. A shading pole piece drive has an inherent natural driving speed and a damping effect opposing any change in this inherent speed. Thus if two or more driving elements are energized at the same time whether adjusted to drive in the same or opposite directions, the damping efiect will oppose changes and thus tend to average all differences. A second characteristic to oppose change in speed is the inertia in the moving parts, mostly in the induction disk, and a third characteristic is friction in the moving parts especially in the gear train and cam shaft. The resultant overall action is a smoothing out of minor irregularities but a quick response to a trend.

The reason for a small area of overlap of the closed positions of contacts Hand 18 pointed out previously is now more easily explained. The opposing action of the two driving elements 13 and 14 controlled by contacts 17 and 18 respectively act as snubs on each other to bring the rotor R to a quick stop in the neutral position and to prevent drifting from the neutral position. The overlap of the closed positions of contacts 17 and 18 is preferable but not essential as previously stated. A gap would not be impractical for commercial use. With a gap the induction disk or rotor would coast an amount dependent upon several variables, one of which is temperature. The larger the gap, the more allowance can be made for coasting but the homing position is less definite. A condition can also occur where the coast of the disk may carry the cam shaft through the gap between the closed positiousof contacts 17 and 18 and set up an oscillating action of the rotor. The limits of the undesirable characteristics of using the gap between the closed positions of contacts 17 and 18 can be held within practical commercial tolerances.

In the form of control apparatus shown by the accompanying drawings and the foregoing description and exainples it. is important to note that response to trafiic variations and the selection of the most suitable offset is based, not on ratios, but on the preponderance of traffic in one direction or the other or the lack of suflicient preponderance in either direction. Take, for example, 20 cars per minute inbound and 10 cars per minute outbound. This gives a preponderance of 10 cars per minute inbound. The ratio in this case of cars inbound to cars outbound is then 20 to 10 or 2 to 1. If there are 15 cars per minute inbound and 5 cars per minute outbound, the preponderance inbound is still 10 cars but the ratio of inbound cars is 15 to 5 or 3 to 1. In an extreme case of 11 cars inbound to 1 outbound, the preponderance of cars inbound is still 10. cars butthe ratio of cars inbound to cars outbound is 11 to 1.

Selection of ofiset based on traffic preponderance is direct and inherent over a continuous range in the equipnient of this invention and is easily adjusted by simple manipulation of not more than four dials. Selection of offset by any known means based on ratios of trafiic in two directions is by steps instead of over a continuous range and the results must be approximated or comprised or both.

A further advantage of equipment in accordance with this invention is that it responds not only to preponderance of traflic in one direction but responds also to the rate of 9 build up of the preponderance. For example, a rapid build up of preponderance of traffic may be experienced following quitting tirne at a large industrial plant or the ending of a public gathering such as an athletic contest. it would not be unusual in such a situation to build up a a preponderance of 30 cars in two minutes which would cause the offset selector to select the oliset favoring this preponderance in two minutes. With the same settings of selector adjustments, proportionally slower build up of preponderance would require a proportionally longer time.

Referring now to FIG. 4, a schematic diagram is shown in block form with equipment of FIG. 1 associated with other units to form a complete signal system.

At the top of FIG. 4 is represented a highway with detectors DO and DI located one in each lane of travel.

Below the highway is represented a master controller MC which may be of any of the various types for maintaining the cycle length of the system. Running out from MC are two lines A and B which, for example, 1 have chosen as two supervisory wire connections as shown in a preferred form of control in my Patent No. 2,657,375. Any of various forms of supervisory control may be employed. Some use more than two interconnecting wires, some use a single interconnecting wire, and some use radio transmission which requires no interconnecting wires at all.

Below and to the right of master controller MC is shown the onset controller C. Gutput from detectors DI and D0 is fed to offset selector ()8 through connections 123 and 122 respectively. Gutput from offset selector OS is fed to latch relays LRI and LRO through connections 125 and 12s res"ectively. Output from latch relays LRZ and LRO feeds lines 3 and 2 respectively, which transmit to local signal controller LSC, shown in block form to the right of the ofiset controller in PEG. Feed from lines 2 and 3 is by taps 127 and 228 which go to the local signal controller LSC. Feed from lines A and B to the local signal controller is through taps 129 and 13b.

in showing the interconnection between offset controller OC and the local signal controller, I have used lines 2 and 3 with two tap-s 1'27 and 12?. This follows a referred method disclosed in my Patent No. 2,657,375 but could be by any of various methods using one or more wires or by radio transmission using no wires.

In the block diagram, FIG. 4., l have indicated a preferred type of local signal controller as disclosed in my Patent No. 2,657,375, but this controller may be of any type of which several are well known.

in the preceding description frequent reference has been made to apparatus of a preferred form and material for the drawings has been selected on this basis. Preferred form, however, is to a large extent a matter of opinion in which there may be sound reasons for difierences. It will be obvious to those skilled in the art that many substitutions or modifications of equipment in addition to those described could be substituted within the scope and spirit of this invention. For example, various means are well known for interval timing which could be substituted for the motors used in the examples such, for example, as timing based on the charge or discharge oi condensers, timing based on mechanical devices, timing based on chances due to heat or timing based on the escape of gas through an orifice. Well lmown substitutions could be made for the driving motors for the cam shafts such as solenoids or pneumatic devices. Springs or other mechanical devices could be used to replace the electrical driving elements used to return the device to a neutral position. Substitutions could be made for cams to operate contacts such as solenoids, or pneumatic, or hydraulic operated cylinders and devices. in the large variety of well known relays are found substitutes for latch relays, and the field of 19 electronics provides many timing means and substitutes for electrical contacts.

While a preferred form of apparatus, together with certain possible modifications, is illustrated, this is by way of example only, and various changes in the organization of parts and in details can be made within the principles of the invention and the scope of the claims.

What I claim is:

1. In a traffic control system having means for detecting tirailic in each of two directions along a highway and providing a like impulse of controlled length for each vehicle, means including a rotor toregister said impulses to compute any excess of trafiic in either of said directions, said rotor being impelled in opposite directions from a neutral point by said impulses resulting firom said vehicles passing in two directions, and electrical means, including contacts opened and closed in response to the direction and degree of rotation of rotor by said impelling impulses to select one of a plurality of trafiic signal offsets including odsets for a neutral position and for opposite directions of rotor displacement.

2. in a traffic control system having means for detecting trafiic in each of two directions alon a highway, means including a rotor to register impulses of controlled length from all vehicles passing in said two directions to compute the preponderance of trailic in either of said two directions, said rotor having a plurality of impelling units, a first and second of which units are disposed to impel the rotor of said device in opposite directions when energized respectively from said impulses from traiiic in said two directions, and a third and fourth of the impelling units being disposed to oppose the actions of said first and second units respectively when energized, and electrical contacts controlled by the rotation of said rotor to energize said third and fourth units.

3. A traflic control system having means for detecting traiiic in each of two directions along a highway and providing a like impulse of controlled length for each vehicle, means to register said impulses from all vehicles passing in said two directions to compute a difierence between traffic in said directions, the last said means including a rotor and a plurality of rotor impelling units, a first and second of said units disposed to impel the rotor in opposite directions when energized respectively from impulses from traflic in said two directions, and a third and fourth of the impelling units being weaker than and disposed to oppose normally the action of said first and second units respectively and to aid the second and first units respectively, and means actuated by movement of said rotor from a neutral position to deenergize the one of said third and fourth units aiding the action of one of said first or second units causing said movement.

4. A trafiic control system as in claim 3 wherein said means is a disk induction motor having shading coils for said third and fourth units adjustable to respond to a said difference of trafiic to return the rotor after rotation thereof by said first or second unit to a neutral position favoring traflic in neither direction.

5. A traflic control system as in claim 3 wherein said means is a disk induction motor adjustable to respond to a predetermined minimum of difference or" traiiic in either direction over that in the other direction to advance the disk as the rotor device to a limiting position of rotation in either direction in accordance with the direction and degree of difference of trafiic, and means to limit the extent of rotation of the rotor in either direction.

6. A traffic control system having means for detecting traliic in each of two directions along a highway and providing a like impulse of controlled length for each vehicle, means to register said impulses from all vehicles passing in said two directions to compute the preponderance of egos-5,1 rs

11 7 traffic in either of said directions, the last said means including a rotor having a plurality of impelling units, a first and second of which are disposed'to impel the rotor in opposite directions when energized respectively from impulses from traific in said two directions, and a third and fourth of the impelling units being weaker than and dis-- posed to oppose the action of said first and second units respectively and to aid the second and first units respectively, and a rotatably mounted cam shaft actuated by said rotor, said cam shaft having cam means to tie-energize the one of said third and fourth impelling units for selected ranges of movement of said cam shaft from a neutral position.

7. A traflic control system having means for detecting traffic in each of two directions along a highway and providing a like impulse of controlled length for each vehicle, means to register impulses from all vehicles passing in said two directions to compare traiiic of said directions, the last said means including a rotor impelled in opposite directions by said impulses from said vehicles passing in two directions, means for selecting trafiic signal ottsets including rotatable cam means driven by said rotor,

relays energized by said cam means to control the se-' lection of traffic signal offsets, and means for latching the contacts of said relays in a predetermined position.

8. A tramc control system having meansfor detecting trafiic in each of two directions along a highway and providing an impulse of controlled length for each vehicle,

means accepting said impulses from all vehicles passing in said two directions to register a difference between trafiic flow in said directions, I

the last said means including a rotor and a plurality of rotor impelling units,

a first and a second of said units energizable by said impulses and disposed to apply like rotor impelling forces in opposite senses when energized respectively by impulses corresponding to trafli-c in each of said directions.

means operative upon rotor displacement from a neutral position in either sense to oppose yieldingly the energized unit causing the displacement and upon de-energization thereof to impel the rotor toward neutral position at a slower rate than the rate of displacement by an impulse; and at least two electrical contact means actuated by said rotor upon rotor displacement in respective senses corresponding to a given excess of traific flow in a. respective direction,

said contact means determining by their relative settings selection of an offset among a preferential offset for each direction of trafiic and a non-preferential offset, in accordance with an excess of traffic in either direction beyond a given minimum excess and a condition of no excess beyond such minimum, said contact means maintaining a relative setting for a predetermined minimum time after cessation of the trafiic excess causing the same,

9. In a tratiic control systenras described in claim 8, said contact means including respective latching relay means energized to actuate latch contacts, offset selection being determined by relative conditions of said contacts, and means on said rotor for unlatching said contacts upon return of the rotor from a displacement causing actuation to a predetermined position before neutral position.

10. A traffic control system having means for detecting traflic in each of two directions along a highway and providing an impulse of controlled length for each vehicle,

'means continuously accepting and opposing said impulses and variable from a neutral condition in opposite senscs in response to impulses resulting respectively from vehicles passing in said two directions,

means responsive to a variation in either sense to diminish the variation at a rate lower than the rate of establishment of a variation by a said impulse,

the means accepting said impulses adapted to accept impulses of opposite sense both simultaneously and suc' cessively to provide a variation representative instantaneously of the net difierence between a residual variation from preceding impulses diminished by responsive means and subsequent impulses,

and switching means actuated respectively by a minimum variation in respective senses from said neutral condition providing by relative conditions of actuation and non-actuation a selection of an offset among two preferential ofifsets for respective directions of trafiic excess and a non-preferential offset.

References Cited in the file of this patent UNITED STATES PATENTS 1,369,204 Koehler July 8, 1919 1,944,723 Stirlen et al. Ian. 23, 1934 2,092,423 Neill Sept. 7, 1937 2,126,431 Von Opel Aug. 9, 1938 2,199,573 Paul May 7, 1940 FOREIGN PATENTS 674,590 Great Britain June 25, 1952 

1. IN A TRAFFIC CONTROL SYSTEM HAVING MEANS FOR DETECTING TRAFFIC IN EACH OF TWO DIRECTIONS ALONG A HIGHWAY AND PROVIDING A LIKE IMPULSE OF CONTROLLED LENGTH FOR EACH VEHICLE, MEANS INCLUDING A ROTOR TO REGISTER SAID IMPULSES TO COMPUTE ANY EXCESS OF TRAFFIC IN EITHER OF SAID DIRECTIONS, SAID ROTOR BEING IMPELLED IN OPPOSITE DIRECTIONS FROM A NEUTRAL POINT BY SAID IMPULSES RESULTING FROM SAID VEHICLES PASSING IN TWO DIRECTIONS, AND ELECTRICAL MEANS, INCLUDING CONTACTS OPENED AND CLOSED IN RESPONSE TO THE DIRECTION AND DEGREE OF ROTATION OF ROTOR BY SAID IMPELLING IMPULSES TO SELECT ONE OF A PLURALITY OF TRAFFIC SIGNAL OFFSETS INCLUDING OFFSETS FOR A NEUTRAL POSITION AND FOR OPPOSITE DIRECTIONS OF ROTOR DISPLACEMENT. 